This invention relates generally to communications and more specifically to communications accomplished via spiral antennas. More specifically, the invention relates to utilizing a spiral antenna design that provides linear polarization. With greater specificity, but without limitation thereto, the invention relates to using two or more linearly polarized, conductor-backed, spiral antennas to simultaneously transmit upon the same frequencies without interfering with each other.
Typically, antennas transmitting simultaneously on the same frequency will interfere with one another. Depending on the relative intensities of the transmissions, one transmission can overwhelm or “drown out” the other transmission.
Certain prior art methods designed to use the frequency spectrum efficiently rely upon complex methods of interlacing messages by time (TDMA) or by coding (CDMA). Another method uses crossed-log periodic antennas. The crossed-log antennas have broad bands and are linearly polarized but are not physically compact. Typically, these antennas extend in the direction perpendicular to propagation on the order of 0.5 wavelength and are often several times the wavelength in size in the direction along the line of propagation. Crossed dipoles and patches are yet a further application. These are relatively compact and are linearly polarized, but are not broad band. Yet another scheme of enhancing communications can be found in the satellite communication field. Antennas used to communicate with satellites often use helices. The uplink signal is typically orthogonal to the downlink signal (e.g. right circularly polarization versus left circular polarization). Helical antennas are rarely compact. The cavity-backed spiral is another design that has been used in many antenna systems. The polarization of a cavity-backed spiral is typically circular and could be used in a dual transmitting mode by transmitting a right-circular polarized signal and receiving a left-circular polarized signal. In the cavity-backed spiral design, half the power utilized is absorbed in the cavity behind the spiral.
There is therefore a need within the art to provide an enhanced method of communicating that permits simultaneous transmission at the same frequencies from a relatively simple antenna system of efficient, compact and broad-band design.